1. Field of the Invention
The present invention relates to a switch for illuminating a knob.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 11-185558 discloses a switch which guides light rays from a light source to a knob via a light guiding member and a lens for illuminating the knob.
The switch is designed such that the incident light rays irradiated from the light source to the light guiding member are further irradiated to the lens from the lower portion at the substrate side. The incident light to the lens, which has been irradiated is guided to the knob so as to be illuminated.
The switch as disclosed above is designed to have the lens moved in association with the operation of the knob. The distance between the lens and the light guiding member for irradiating the light rays from the light source toward the lens varies as the knob is operated.
For example, when the knob is depressed to bring the lens into close to the light guiding member, the distance between the lens and the light guiding member is reduced to allow incidence of more light rays to the lens, thus increasing illumination luminance for the knob. When the lens is moved away from the light guiding member, the distance between the lens and the light guiding member is increased to reduce the amount of incident light rays to the lens, thus lowering illumination luminance for the knob.
Accordingly, the switch as disclosed in Japanese Unexamined Patent Application Publication No. 11-185558 changes the amount of incident light to the lens upon operation of the knob, thus largely changing the illumination luminance for the knob.
Accordingly, the switch designed to illuminate the knob is required not to largely change the illumination luminance for the knob upon its operation.